Survivability of conidia from a recombinant Aspergillus oryzae strain overproducing cellulase, and its parent strain in a soil environment

A recombinant Aspergillus oryzae strain TB1 produced by Kitamoto et al. (1999) overproduces cellulase 500-fold higher than its parental strain KBN616-39. Strain TB1 was reported to decrease soy sauce refuse, when it was used in production of soy sauce in a small scale experiment. To determine the survivability of the conidia of strain TB1 together with its parental strain KBN616-39 and a wild type strain PTR-1, they were inoculated in black soil packed in plastic tubes as a soil environment and incubated at 25 deg C. Colony formation was determined using the dilution plating method. Repetitive survivability experiments showed that the average survivability-decreasing rates and dispersion of strain TB1 were the same as strains KBN616-39 and PTR-1, where they survived over seven weeks at 25 deg C in the soil environment. None of the strains showed an increase in colony formation. Thus, we suggest that their conidia neither germinate nor grow in soil.